Don't understand about inlets and vents on furnaces; can someone explain?

Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Don't understand about inlets and vents on furnaces; can someone explain?

They seem very fussy about acceptable terminations on vents and inlets. Trane requires a vent coming straight out of the wall to be 12" min and 14" max. What would the harm be in running the vent out 30"? All I can think of is condensation, but they let you angle it down, so any condensation would run out.

I am sure there is a really good reason, but its not clear to me what that might be.

sticking further out from the wall along with the risk of freezing would be a hazard for trip fall or something banging into and breaking it. how would it be supported?

why would you want it out that far?

At present, the vent and inlet are under my deck. The inlet has twice picked up moisture from the vent, which has frozen and stopped the furnace. I have to go out every 8 hours to scrap.

The piped are not installed properly, according to Trane's specs. They are too close to the deck, too close to a side wall, too close together, and the vent is not long enough. With so much wrong, a problem had to happen.

If the vent was extended a couple feet, the inlet would not be sucking in the exhaust, as it is now. Supporting from the deck would be easy enough, and no one goes under it.

If extending and insulating the vent a few feet is acceptable,then that is a quick and inexpensive solution. If the whole piping system has to be rebuilt to be in compliance, then it would be very expensive.

The system could have been in compliance; I don't know why they crammed it into that corner.

extending and insulating the exhaust would probably help.
pics would be good so we see what you're dealing with.

You can see it is too close to the deck, too close to the side wall, too close together, and the vent is too short.
Extending the vent 2 feet would, I expect as someone ignorant on the subject, solve the problem.
IF it is an acceptable solution.

According to the installation instructions, it can be set up as a single pipe, getting the combustion air from the basement. That would imply (again to an ignorant person) that extending the vent 2 feet wouldn't hurt anything.

We did one where we exited the house under a deck, we insualted it with armiflex and ran it our from under the deck. Never had a problem and it extended about 12' out the north side of the house under the deck.

In order to vent underneath a deck, it must be open on 2 sides.
You can extend the vent pipes to the edge of the deck, and there is an insulation product called arma-flex which will fit the pipe properly.
You must extend both pipes in order for the termination to be correct.
The reason trane or any other manufacturer wants their pipes a certain way is so they terminate in the same "pressure zone".
Having one pipe under the deck and one exposed, can mess with the pressure switches/inducer motor during periods of high winds.
Your other option would be to "snorkel" both pipes up above the deck.

I'd also like mention going to a single pipe setup is not advisable.
You CAN do it, but then you have to cut a new 5 or 6" hole in the side of your house to provide this combustion air supply to your furnace room.

1) He conceded the inlet had a lot of ice in it. At first he insisted it was sucked in snow, but eventually agreed it was frozen exhaust.
2) He agreed the vent was too short. He lengthened it from 8" to 14".
3) He agreed the pipes were a bit too close together. He turned the inlet 90 fitting away from the vent, thinking that would help
4) He disagreed about the required distance from the deck and the inside corner, saying those were a matter of code, which he didn't know right off hand.
5) He did not think it posed a threat to the heat exchanger. He says those are continually bathed in acidic condensate, so a bit more from the inlet won't matter.
6) He agreed that the system had 43 of the allowed 50 feet of pipe, so there was room to extend them past the deck.

I agreed to run it this way and see if I continued to get ice. He agreed to see if he could find 2" armaflex to extend the pipes a few more feet. Although the deck is 6', the wall the pipes are next to is only 3', so if we could get out to the wall; that ought to be okay. I think.

I have some questions:
A) Is #3 acceptable? It is shown as straight down in the installation manual, but it is well protected from snow, so maybe it is okay turned?
B) What is code for distance from inside corner and overhang typically?
C) Any truth to what he is saying about the #5?

1) He conceded the inlet had a lot of ice in it. At first he insisted it was sucked in snow, but eventually agreed it was frozen exhaust.
2) He agreed the vent was too short. He lengthened it from 8" to 14".
3) He agreed the pipes were a bit too close together. He turned the inlet 90 fitting away from the vent, thinking that would help
4) He disagreed about the required distance from the deck and the inside corner, saying those were a matter of code, which he didn't know right off hand.
5) He did not think it posed a threat to the heat exchanger. He says those are continually bathed in acidic condensate, so a bit more from the inlet won't matter.
6) He agreed that the system had 43 of the allowed 50 feet of pipe, so there was room to extend them past the deck.

I agreed to run it this way and see if I continued to get ice. He agreed to see if he could find 2" armaflex to extend the pipes a few more feet. Although the deck is 6', the wall the pipes are next to is only 3', so if we could get out to the wall; that ought to be okay. I think.

I have some questions:
A) Is #3 acceptable? It is shown as straight down in the installation manual, but it is well protected from snow, so maybe it is okay turned?
B) What is code for distance from inside corner and overhang typically?
C) Any truth to what he is saying about the #5?

I appreciate your help.

A) it is acceptable, but ideally it is still tilted downwards to some degree
B)36" is code, however the install manual will indicate if there's any other considerations.
C) the secondary HX is the only part exposed to the condensate. The burners, and primary HX is not built to handle corrosive gasses. It will rot the steel within a few years.

A) it is acceptable, but ideally it is still tilted downwards to some degree
B)36" is code, however the install manual will indicate if there's any other considerations.
C) the secondary HX is the only part exposed to the condensate. The burners, and primary HX is not built to handle corrosive gasses. It will rot the steel within a few years.

Would that be apparent after 6 heating seasons? I purchase the 6 year old house subject to a cleaning and satisfactory inspection by the installer. If the damage should be apparent, then either it isn't damaged or he lied about it.

Ballpark, what the the cost, parts and labor, be for a new burner and primary HX?